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<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
 <script>
    var num1=100.1
    var num2='100.1abc'
    var num3='abc100.01'
    console.log(parseFloat(num1))
    console.log(parseInt(num1))
    console.log(parseFloat(num2))
    console.log(parseInt(num2))
    console.log(parseFloat(num3))
    console.log(parseInt(num3))

    //NaN not a number

    var num4=100.01
    console.log(typeof num4.toString())

    // string 函数/方法
    var str1 ='abcdefg'
    console.log(str1.length)

    var str2 ='9999cbshbc'
    console.log(str1.concat(str2))
    console.log(str1+str2)
    var str3 ='bcjbjawbdfjfkbjkmlkfllmnebdujwqhd'
    console.log(str3.indexof('w'))
    console.log(str3.lastIndexOf('w'))


    var str4 = 'sncdkvmdvdkll'
     str4=str4.replace('snc','6')
    console.log(str4)

    var str5 = 'Asjkkdnkm'
    console.log(str5.toUpperCase())
    console.log(str5.toLowerCase())

    var str6 = 'q w e r t '
    var str7 = 'aa=bcv&ks=lnn&cc=ttt'
    console.log(str6.split(' '))
    console.log(str7.split('&'))

    var str8='bweahaqbnlknllmljqw'
    console.log(str8.slice(4,8))  //[4,8)
    //库  数学库
    var num5 = 100
    console.log(Math)
    console.log(Math.abs(-100)) //绝对值
    console.log(Math.ceil(9.0000001))
    console.log(Math.floor(9.99999999))

    console.log(Math.max(-100,100,300))
    console.log(Math.min(-100,-300,0))

    console.log(Math.pow(2,4)) 
    console.log(Math.pow(10,3))
    console.log(Math.sqrt(4,2))
    console.log(Math.random()) //0-1
    console.log(Math.random()*20) //0-20
    //5-25 ???
    console.log(Math.random()*20+5)
//
    console.log(Array.isArray('abc'))
    console.log(Array.isArray([1,2,3,4]))

    console.log(Array.of(1,2,3,4,5,6,7,8,8))

    console.log(Array.from('abc'))

    var arr1 = [1, 2, 3, 4, 5]
        console.log(arr1.pop())
        console.log(arr1)  //[1,2,3,4]
        console.log(arr1.push(100))
        console.log(arr1)  //[1,2,3,4,100]
        console.log(arr1.shift())
        console.log(arr1) //[2,3,4,100]
        console.log(arr1.unshift(400))
        console.log(arr1)
        //pop 删除数组末尾元素 
        //返回被删除的元素
        //push 数组末尾添加元素    
        //返回添加完成后数组的长度
        //shift 删除数组首位的元素 
        //返回被删除的元素
        //unshift 往数组首位添加元素
        //返回添加完成后数组的长度
        console.log(arr1.length) // 5
        //往数组任意位置添加或者删除元素
        var arr2 = [1, 2, 3, 4, 5, 6, 7]
        console.log(arr2.splice(2, 3, 100, 200, 300, 400, 500, 600))  //起始位置   长度
        console.log(arr2)
        var arr3 = [1, 2, 3, 4, 5, 6, 7]
        arr3.splice(3, 0, 100)
        console.log(arr3)  //[1,2,3,100,4,5,6,7]
        arr3.splice(5, 1)
        console.log(arr3)
        var arr4 = [1, 2, 3, 4, 5]
        console.log(arr4.reverse())
        console.log(arr4)
        var arr5 = [4, 3, 2, 20, 5, 7, 14, 3, 4, 21, 2, 5, 3]
        arr5.sort(function (a, b) {
            return b - a
        })
        console.log(arr5)
        var arr6 = [1, 2, 3, 4, 5]
        arr6.fill(100, 2, 4)  //[)
        console.log(arr6)
        var arr7 = [1, 2, 3, 4, 5, 6, 7]
        console.log(arr7.slice(3, 5))  //[3,5)
        console.log(arr7)
        var str10 = 'a b c d e f g'
        var arr10 = str10.split(' ')  
 
        console.log(arr10.join('-'))  
       

 </script>   
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